Ethylene dichloride (1,2-dichloroethane) is an important starting material in the production of chlorinated hydrocarbons such as vinyl chloride, vinylidene chloride, methylchloroform, trichloroethylene, and perchloroethylene.
Ethylene dichloride is typically produced by reacting ethylene and chlorine in a liquid reaction medium or by an oxyhydrochlorination process wherein a gaseous mixture of ethylene, hydrogen chloride, and oxygen is contacted with a Deacon-type catalyst at a moderately elevated temperature.
The crude product obtained by the oxyhydrochlorination process typically assays about 97 percent ethylene dichloride and contains a number of impurities chief among which are chloroform, carbon tetrachloride, trichloroethylene, and 1,1,2-trichloroethane.
Since the purity and quality of chlorinated hydrocarbon products produced from ethylene dichloride depend on the purity of the latter, the crude ethylene dichloride must be further processed to remove or reduce the level of impurities.
Ethylene dichloride is typically purified by distillation; however, distillation is complicated by the fact that carbon tetrachloride forms an azeotrope with ethylene dichloride. Since carbon tetrachloride and chloroform are removed as light fractions upon distillation of ethylene dichloride, considerable amounts of ethylene dichloride are lost in the light fraction or distillate due to azeotropic entrainment with carbon tetrachloride. For example, a typical light distillate has been found to contain from 40 to 50 weight percent and as much as 90 weight percent ethylene dichloride.
It is desirable, therefore, to devise means of breaking the ethylene dichloride-carbon tetrachloride azeotrope to minimize loss of ethylene dichloride in the light distillate while still enabling substantially complete removal of chloroform and carbon tetrachloride impurities.